Bitcoin Forum

1. Why the f# didn't they add the option to use also bitcoin addresses (instead of only public keys) to create multisig addresses? I am sure there must be a strong reason but I don't see it at the moment. Many users don't know their public keys immediately, and some (e.g. Circle etc.) don't know them at all.
2. When a multisig transactions has been partly signed, how can the other allowed signatories be notified? (besides emailing them).

If someone can't give you their pubkey then they almost certainly cannot sign for a multisig. You cannot just go and grab random keys from people and expect them to be able to use them in random ways!   Thats handing someone a safe and saying "what do you mean you can't open it? it's keyed with a fragment from your DNA; you've got like a trillion copies of that inside you!"; beyond the basic bit of protection from doing something boneheaded there, using hash160s there would basically double the amount of data needed in the blockchain for a multisig transaction; and would much more rapidly run into the redeemscript size limits.

For (2) thats up to the software you're using.

Thanks gmaxwell.
Re 2- is there a hosted wallet with a simple UI to retrieve a public key and sign a multisig transaction?

there was a website that helped with multisig, but I can't find it now, I'll edit the post if I find! Armory also has lockbox UI... Maybe it can help you using multisig :)

I spent a good few hours yesterday learning multisig. It was really fun, but that's because I like troubleshooting, digging for info and learning new things. It's actually pretty cool once you get the hang of it. It's a bummer they haven't added any UI for multisig on the bitcoin core client yet, but I think they have more important/high priority things to work on that's not multisig.

Now that most P2SH redeem scripts are standard you can create multisig scripts which uses addresses (pubkehash) instead of pubkeys.  Client support for signing that script is another thing.  So this is more a client implementation detail not a protocol limitation.